Sea Ice Extent Sea Ice Concentration Access Data  
Sea Ice Extent Trends
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Numeric data of sea ice extent in the Arctic and Antarctic Ocean (TSV file)
  • Data from November 1, 1978 to December 31, 2012 are included.
  • The format is "month, day, year, extent (unit: square km)
  • Number "-9999" represents that we couldn't conduct the observation during the period for the reason that the satellite went into constrained operation mode or stand-by mode to avoid harmful effects by meteor showers and solar flares.
  • To use the data of Sea Ice Concentration(binary format) and Sea Ice Extent area(text format), please take a user registration as described here.
Notes on the sea-ice extent data
  • The sea-ice extent is calculated as the areal sum of sea ice covering the ocean where sea-ice concentration (SIC) exceeds a threshold (15% for AMSR-E). SICs are derived from various satellite-borne passive microwave radiometer (PMR) sensors using the algorithm developed and provided by Dr. Comiso of NASA GSFC through a cooperative relationship between NASA and JAXA. The following sensor's data were used;

    •Nov. 1978 - Jul. 1987:SMMR
    •Jul. 1987 - Jun 2002:SSM/I
    •Jun. 2002 - Oct. 2011:AMSR-E
    •Oct. 2011 - the present:WindSat

  • In order to eliminate calculation errors due to a lack of data (e.g., for traditional microwave sensors such as SMMR and SSM/I),sea-ice extent is defined as a temporal average of several days. In this data, we adopt the average of five days.
Definition of sea-ice cover (extent and area)
  • The area of sea-ice cover is often defined in two ways, i.e., sea-ice "extent" and sea-ice "area". These multiple definitions of sea-ice cover may sometimes confuse data users. The former is defined as the areal sum of sea ice covering the ocean (sea ice + open ocean), whereas the latter "area" definition counts only sea ice covering a fraction of the ocean (sea ice only). Thus, the sea-ice extent is always larger than the sea-ice area. Because of the possible errors in SIC mentioned above, satellite-derived sea-ice concentration can be underestimated, particularly in summer. In such a case, the sea-ice area is more susceptible to errors than the sea-ice extent. Thus, we adopt the definition of sea-ice extent to monitor the variation of the Arctic sea ice on this site.